1. Field of the Invention
The present invention relates to the field of high-density data storage and more specifically to a data storage medium, a data storage system, and a data storage method.
2. Description of Related Art
Current data storage methodologies operate in the 0.1-10 μm regime. In an effort to store ever more information in ever-smaller spaces, data storage density has been increasing. In an effort to reduce power consumption and increase the speed of operation of integrated circuits, the lithography used to fabricate integrated circuits is pressed toward smaller dimensions and denser imaging. As data storage size increases and density increases and integrated circuit densities increase, there is a developing need for compositions of matter for the storage media that operate in the nanometer regime.
A storage device for storing data based on the atomic force microscope (AFM) principle is disclosed in “The millipede—more than 1,000 tips for future AFM data storage” by P. Vettiger et al., IBM Journal Research Development, Vol. 44, No. 3, March 2000. The storage device has a read and write function based on a mechanical x-, y-scanning of a storage medium with an array of probes each having a tip. The probes operate in parallel with each probe scanning, during operation, an associated field of the storage medium. The storage medium comprises a polymer layer. The tips, which each have an apex diameter between 5 nm to 20 nm, are moved across the surface of the polymer layer in a contact mode. The contact mode is achieved by applying small forces to the probes so that the tips of the probes can touch the surface of the storage medium. For that purpose, the probes comprise cantilevers, which carry the tips on their end sections. Bits are represented by indentation marks or non-indentation marks in the polymer layer. The cantilevers respond to these topographic changes while they are moved across the surface of the polymer layer during operation of the device in read/write mode.
Indentation marks are formed on the polymer surface by thermomechanical recording. This is achieved by heating a respective probe operated in contact mode with respect to the polymer layer. Heating of the tip is achieved via a heater dedicated to the writing/formation of the indentation marks. The polymer layer softens locally where it is contacted by the heated tip. The result is an indentation, for example, having a nanoscale diameter of the tip that is used in its formation, being produced on the layer.
Reading is also accomplished by a thermomechanical concept. The probe is heated using a heater dedicated to the process of reading/sensing the indentation marks. Either a separate heater is used, which is not connected to the tip and therefore the probe is not heated or the probe is heated but not so as to cause heating of its associated tip, that is, the heating temperature is not high enough to soften the polymer layer as is necessary for writing. The thermal sensing is based on the fact that the thermal conductance between the probe and the storage medium changes when the probe is moving in an indentation as the heat transport is in this case more efficient. As a consequence of this, the temperature of the heater decreases and hence, also its electrical resistance changes. This change of resistance is then measured and serves as the measuring signal.
For such thermal probe storage applications, the media requirements are defined by the indentation mechanics of polymers and the need to limit media and tip layer. Preferably, the glass transition temperature should be minimized but the polymer should also be thermally stable. Thermal stability of polymers is achieved by crosslinking and using polymers with exceptional thermal stability. Crosslinking typically produces hard materials that require high forces to form indents and therefore lead to increased tip wear. With moderate write speeds, one may use higher temperatures to minimize forces and tip wear. Since the write temperature increases with the write speed, this trade-off between heat and force is not possible for fast writing which requires operation of the cantilever heater element at its maximum design temperature.
Accordingly, it is desirable to provide a method of producing a data storage medium which reconciles the conflicting requirements of high crosslink density for media wear resistance and low glass transition temperature for soft writing conditions.